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b=jgW0MiyEc84udzOs8HZR9dgF6PsfXdc1zq8rKL0vNRui3W6wPWQzdBmKIQK+/fGkh Oj42OYChE/IhgPBCUOmMsOm2djzavBzqNer80aB+K2rSMiYlM0dRl8KQxbFTGdK+Wa ocrsvtnYADmJwOUwzAoBQ6BJndJaJ7msgNTQPcZg= Date: Sun, 27 Apr 2025 17:25:51 -0700 From: Andrew Morton To: Guilherme Giacomo Simoes Cc: pasha.tatashin@soleen.com, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Subject: Re: [PATCH] mm: alloc_tag: change the KASAN_TAG_WIDTH for HW_TAGS Message-Id: <20250427172551.fbf81f14d4e6563c13007a65@linux-foundation.org> In-Reply-To: <20250426180837.82025-1-trintaeoitogc@gmail.com> References: <20250426180837.82025-1-trintaeoitogc@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6ADC61A0002 X-Stat-Signature: gmiadwqqhjnch6fsd787uweocuq6yr63 X-Rspam-User: X-HE-Tag: 1745799953-551836 X-HE-Meta: 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 obGhFcvO Wi7qo X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 26 Apr 2025 15:08:37 -0300 Guilherme Giacomo Simoes wrote: > the KASAN_TAG_WIDTH is 8 bits for both (HW_TAGS and SW_TAGS), but for > HW_TAGS the KASAN_TAG_WIDTH can be 4 bits bits because due to the design > of the MTE the memory words for storing metadata only need 4 bits. > Change the preprocessor define KASAN_TAG_WIDTH for check if SW_TAGS is > define, so KASAN_TAG_WIDTH should be 8 bits, but if HW_TAGS is define, > so KASAN_TAG_WIDTH should be 4 bits. Why? I assume the effect is to save a few flags bits under some circumstances? But that's just me guessing - please fully describe the motivation and effects within changelogs.